論文

This study investigated experimentally a response of premixed Bunsen flame to transient change in a fuel composition and a method to control the variation. Fuel mixtures were composed of methane, ethane and propane. The volumetric fraction of methane was varied from 92 % to 76 % by 4 % and the ethane/propane ratio was 5. Transition time of the fuel composition was 1, 5, 10 and 20 s. Flow velocity and the equivalence ratio were 0.8 m/s and 0.85 respectively before the transition. Channel length L between the merging point of fuels and the point of air was 0, 500, 1000, 1500 mm. The motion of flame was recorded by a high-speed video camera at 60 fps. The experiment was conducted under the fuel flow rate constant and the equivalence ratio constant conditions. In the former condition, the flame height varied almost linearly not depending on the conditions. In the latter condition, variation of the steady flame height was smaller than the former condition. However, the unsteady flame height exceeded or fell below temporarily the steady flame height. This is due to the time lag between the transmission of fuel flow rate variation and fuel compositions variation. Therefore, considering this time lag, the experiment was conducted with a system which had a density meter to detect the fuel composition variation. The system controlled automatically the fuel flow rate. At long L and short transition time, there were some peaks in the flame height variation. It is considered that this is caused by the difference between the actual density and the output of the density meter due to Taylor dispersion and response time of the density meter. However, the flame height variation was smaller than the variation without control, and particularly at long transition time, the variation was suppressed sufficiently.

The effects of co-doping in phosphors and the use of co-doped phosphors to extend the temperature measurement range were experimentally investigated in terms of the lifetime method. Such effects can be evaluated by comparing the single and double luminescent centers. In this study, YAG:Tb, YAG:Cr and YAG:Cr,Tb were prepared by sol-gel method and the luminescence intensity was measured under excitation by the 4th harmonic of Nd:YAG laser. In order to improve the temperature measurement performance of YAG:Cr,Tb, it is desirable to divide it into two wavelength regions with a threshold around 600 nm, and to switch between the two regions depending on the temperature range when performing temperature measurement by the lifetime method. The absolute lifetime sensitivity SA is a suitable index to use when dividing the temperature region into two regions, resulting in switching at around 800 K. The lifetime of the Cr-derived luminescence is slightly longer, while that of the Tb-derived luminescence is about 10 times shorter.

The purpose of this study was to improve the accuracy of knock detection for lean burn SI engines. In this study, we conducted an experiment to observe autoignition in an engine cylinder using a borescope and a high-speed camera under an air excess ratio of 2.1. In addition, the resonance frequency of each vibration mode by knocking and the knock intensity were also calculated from the in-cylinder pressure history. Autoignition was optically observed in all cycles with a knock intensity of more than 20 kPa or more, and in some cycles with that of less than 20 kPa. We compared the vibration caused by combustion and it caused by autoignition. As a result, by distinguishing between the vibration caused by combustion and it caused by autoignition using window functions, a knocking cycle that could not be detected by the conventional index was detected.

The flame temperature of a laminar premixed flame with continuous convex and concave curvatures was experimentally investigated. The flame temperature and the stretch rate along the flame surface were measured for the flame formed in the lean propane/air mixture (φ = 0.72, Lc = 1.74). As a result, the flame temperature at the convex toward the unburned mixture was lower than the adiabatic flame temperature and that of the concave was higher, because of the flame stretch and the Lewis number effect. However, the measured flame temperature was different from the estimated flame temperature by the theory for the local flame structure proposed by C. J. Sun et al. We guess the reason why such difference was arisen is the existence of the heat transfer along the flame surface, so we suggest that the heat transfer along the flame surface should be considered in the case of the flame with continuous convex and concave curvatures.

Heat transfer inside an engine has been studied for improving thermal efficiency by mitigation of the cooling loss. Flow near a piston top and heat flux on it were simultaneously measured with a microPIV and a MEMS thin film sensor in a motoring mode of an optical engine. It was confirmed that averaged heat flux over -15~15 CA deg. showed a positive correlation to the normal flow fluctuation, and that the instantaneous wall heat flux showed obvious correlation to the instantaneous normal velocity at 0.5 mm above the wall with a time lag of 200 s level. Moreover, a combination analysis of the wall parallel velocity and FFT spectrum of the heat flux showed that the fluctuation in the heat flux is composed of temperature unevenness of several millimeter scale and eddy motion of several hundred micrometer.

In order to understand the effect of velocity boundary layer on the heat loss in a tumble enhanced engine, simultaneous measurements of high-speed microscopic particle image velocimetry (PIV) near the piston top and a micro electro mechanical systems (MEMS) heat flux sensor on the piston surface was conducted in the motored optical engine with enhanced tumble flow. This engine was rotated at2000 rpm. Experimental results show the correlation between the velocity fluctuation and the peak value of heat flux, and the correlation coefficient shows higher value at 0.50 mm from the piston wall rather than 0.27 mm and 0.12 mm.

The influence of burner rim thickness on the stabilization mechanism of methane diluted with nitrogen and air jet diffusion flame was investigated experimentally. The diffusion flame was stabilized on a two-dimensional Wolfhard-Parker burner with a variable partition wall (burner rim) thickness between the fuel and air jets. The diffusion flame on a thin burner rim showed a blowout at the stability limit, which occurred after the lifted flame behavior. For a thick burner rim, the flame base remained well anchored in the wake region, and a blowoff occurred suddenly and not via the lifted flame with an increase in the jet velocity. For moderate rim thickness, a transition from-a wake-anchored flame to a lifted flame appeared (liftoff), and blowout then occurred as the jet velocity increased. The blowout limits of lifted flames were not influenced by rim thickness; however, the blowoff,limits were extended with an increase in the rim thickness. Particle image velocimetry (PIV) measurements showed that unburned flow entrainment into the base of the lifted flame was of the same order of magnitude as the propagation speed of the premixed flame. Therefore, the stabilization of the lifted diffusion flame for a thin rim might be determined by the premixed propagation of the flame base. On the other hand, a flame base anchored on the thick burner rim experienced a velocity distribution similar to a counterflow. Furthermore, the stretch rates at the liftoff and blowoff limits agreed well with the extinction limits of ordinary counterflow diffusion flames. Thus, their mechanisms could be explained by flame stretched extinction. (c) 2009 The Combustion Institute. Published by Elsevier Inc.-All rights reserved.

A low-swirl burner operating in premixed mode with methane and air is studied using high-speed acetone and OH-PLIF and advanced post-processing methods. In a transient operating point where the equivalence ratio is slowly increased while keeping the bulk velocity constant, a thermo-acoustic instability is found to grow and generate large pressure fluctuations in the combustion chamber. The instability is maintained by bursts of flame in phase with the pressure fluctuation cycle. It is found that these bursts are amplified by the fact that the boundaries of the flame arms are fluctuating in phase. This phasing of the arms' boundaries is due to the change in flame speed coming from the increase of equivalence ratio.

Copyright © 2019 The Society of Chemical Engineers, Japan Fluid flow patterns with a gel reaction in a circular flow pipe are investigated experimentally. Solutions of 10 mass% polyvinyl alcohol (PVA) and 3 mass% borax are used as the working fluids. The flow channel consists of a transparent main flow pipe and a transparent branch flow pipe that is connected vertically to the main flow pipe. The solution of 10 mass% PVA flows in the main flow pipe under steady-state conditions. The Reynolds number (Rem) based on the mean velocity and the diameter of the main flow pipe is less than 30. The borax solution is colored with blue dye to visualize the flow patterns and is injected once only from the branch flow pipe. The experimental results show three distinct flow patterns, namely, capsule, capsule+stretched, and capsule+stretched+fingering flow. Rem and the ratio of the volume flow rate (β) are used to predict quantitatively the flow patterns with gel reaction. The results show that, in the region in which β is less than unity, capsule flow forms and β is the governing parameter. In the region in which β is greater than unity, Rem is dominant for determining the flow pattern with gel reaction.

© 2020 IOP Publishing Ltd. The precision of the lifetime method in phosphor thermometry was examined in terms of the uncertainty in temperature prediction. Such uncertainty can be estimated using the rate of change in lifetime with temperature (lifetime sensitivity) and the uncertainty in measured lifetime. This uncertainty depends on phosphorescence characteristics such as phosphorescence intensity and lifetime decay shape. In this study, we proposed a method of calculating uncertainties in measured lifetimes by the estimated regression coefficients in measured decay signals of phosphors. To demonstrate this evaluation, the uncertainties in the predicted temperatures of some common phosphors (MFG, GGG:Cr, Y2O3:Eu) were calculated. Consequently, the temperature predictions by the lifetime method with MFG, GGG:Cr, and Y2O3:Eu showed high precision at about 800 K, 700 K, and 900 K, respectively. This method of evaluating precision by using both lifetime sensitivity and uncertainty in lifetime helps to improve the appropriate use of phosphors for the lifetime method in phosphor thermometry.

© 2019 SAE Japan and SAE International. The thermal efficiency of internal combustion engines can be improved dramatically with the right combination of engine technology and fuel technology. Super lean-burn technology is attracting attention as a means of boosting thermal efficiency. However, there is a limit to how lean a fuel-air mixture can be before combustion becomes unstable or misfire occurs. The authors evaluated the effects of various chemical compositions on the lean limit under super lean-burn conditions. By changing the composition of the fuel, it was possible to achieve excess air ratios of over 2.0, resulting in high thermal efficiency.

The characteristics of a medical heat and moisture exchanger with filter (HMEF) that contained polyurethane sponges and CaCl2 were investigated experimentally and model analysis was performed. Variations in the temperature and humidity were measured. Saturated air at 37 °C simulating exhalation and dry air at 26 °C simulating inhalation were fed alternatively through the HMEF in opposite directions. The period was set as 256 s, 64 s, 16 s and 4 s. When the period was long (256 and 64 s), the polyurethane sponges and CaCl2 played an important role in condensation and evaporation of water and the amplitudes of the temperature variation was so large that it overshot the input condition. When the period was shortened (4 s), the amplitudes of the temperature and humidity variations decreased and the relative humidity of the patient side of the HMEF gradually reached that of the exhalation conditions. This suggests that the characteristic times of condensation and evaporation were longer than that of the respiration (τb = 4 s). In other words, the unsteady effect is important for the condensation and vaporization mechanism of HMEF. The mechanism was supported by the model analysis. In addition, comparing the results of the experiments and model analysis elucidated the effect of the connecting pipe, which corresponds to the dead space effect in clinical use.